MB-100: refactored read-only admin management ui

Particularly I wasn't comfortable with having ro admin name cells at
core-data level.

New code moves all corresponding cells info account management
sub-section.

It also ensures that cells are refreshed on leaving/entering account
management tab. For that to work well it places spinner on user
management form when user management data is loaded.

Also given that we dont really need "isROAdminExists" on pools reply
it removes it.

Change-Id: I8fb12f71e1e0626857a5b25b2176b3ddcb6d4cfd
Reviewed-on: http://review.couchbase.org/28251
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Pavel Blagodov <stochmail@gmail.com>